The invention deals generally with an air-conditioning plant for motor vehicles and especially with an air-conditioning plant which is intended for buses. A typical air-conditioning plant of this type has a condenser and an evaporator which are disposed partitioned, side by side, in trough-like housings. The condenser has a large-surface condenser block extending transversely to the direction of travel and inclined downwards in the direction of travel and contains condenser fans which carry off the condenser exhaust air to the outside. The evaporator contains evaporator blocks extending in the direction of travel and disposed at a distance transversely to the direction of travel. Furthermore, a fresh air intake space is associated with the evaporator part by way of which fresh air is drawn in by means of evaporator fans which also convey the air, after it has passed through the evaporator, as conditioned air into an air channel of the vehicle which extends in the longitudinal direction of the vehicle at the transition are between the roof and lateral surfaces of the motor vehicle.
From the German Offenlegungsschrift 32 24 895, an air-conditioning plant for motor vehicles of the previously mentioned type has been known which is intended especially for buses. This air-conditioning plant is intended for on-roof mounting and is designed to have a flat configuration. Despite the provision of a flat configuration, it has turned out, however, that there are applications when the height above the roof, especially in the case of buses, will be limited by regulations in such a way that the known air-conditioning plant cannot be used for on-roof mounting, since it leads to a superstructure height above the roof that is too great. Furthermore, in the case of the known air-conditioning plant, the condenser and the evaporator are mounted lying one behind the other on the roof in the direction of travel, and trough-shaped housing parts of the condenser part and the evaporator part are attached to the contour of the roof. Since the plant, as a whole, is mounted on the roof of the vehicle, arrangements must be provided for carrying off rainwater as well as arrangements for carrying off condensation water which occur in the air-conditioning plant.
From the German Offenlegungsschrift 27 57 415, another air-conditioning plant has been known for mounting on the roof wherein the condenser block is aligned approximately edgewise and is inclined upwards at a steep angle in the direction of travel. However, difficulties result in the situation where large heat condenser exchange surfaces must be accommodated to achieve a relatively high cooling capacity. The length of the condenser block is predetermined by the maximum width of the vehicle, and the height should be as small as possible, not only for esthetic reasons but also with a view to a favorable air resistance number (C.sub.w), so that the total weight of the air-conditioning plant in excess of the standard measure of height of the vehicle should not be considerably greater. However, if the condenser block is enlarged in the direction of depth, since the hind rows of pipe contribute a comparatively small amount to the total performance, an unfavorable ratio of weight, price and performance of the condenser will result. Additionally with a depthwise enlargement, the air flow resistance of the condenser will also become greater so that fans with a higher performance will be required as a countermeasure, as a result of which the weight and the costs of the installation will increase.
From the German utility Pat. No. 77 14 617, an air-conditioning plant has been known for mounting on the roof which has two parallel condenser blocks extending in the direction of travel. Since the height is limited, the heat exchanger surfaces can be enlarged only by extending either the length or the depth. This, in turn, leads to relatively deep condenser blocks. Additionally, an increased air resistance has to be overcome in the condenser, since deflections of air are needed.
In view of the foregoing, the invention has a primary object of developing an air-conditioning plant for motor vehicles of the initially mentioned type which will have a favorable ratio of cooling efficiency, weight and price, a height that is as small as possible especially a decreased height above the vehicle roof as compared to the air-conditioning plant according to the German Offenlegungsschrift 32 24 895, and will be integratable into the skeleton of the roof construction without any significant changes.
It is a further object to provide an air-conditioning plant which can be built-in, especially in the tail area of a vehicle, with only slight height of construction above the roof while also taking into consideration the fact that a sufficient height for standing up is ensured, especially in the aisle of the passenger compartment of the vehicle.
Additionally, it is preferable to enable an admixing of fresh air via the air-conditioning plant. Moreover, not only should the plant be designed flat, but also compact in its total dimensions in order to take into account the available limited conditions of space. For example, according to special regulations, it is required that the height of construction above the roof of the vehicle may run maximally to 127 mm.
In this respect, applicant's motor vehicle air-conditioning plant is distinguished by the characteristics that the condenser is inclined downwardly in the direction of travel and is partially under the level of the roof construction of the vehicle in the rear area of the vehicle; that the evaporator part is disposed, in a direction toward the vehicle interior, below the condenser; that the evaporator blocks of the evaporator are disposed at such a distance from one another that a channel-shaped interval remains free between them; and that the condenser fans are disposed behind the condenser in the rear area.
In the case of the air-conditioning plant of the invention, an efficient large-surface condenser block of flat construction has been provided for the condenser part, whereby the condenser part with the condenser trough is partially lowered below the roof level, in order to achieve the desired construction height above the roof without any loss in cooling performance and without reduction of the effective heat exchange surfaces. The large-surface condenser block, in this case and viewed in the direction of forward travel, is disposed inclined downwards in order to enable the entire heat exchange surface to be acted upon relatively evenly by air in order to ensure a complete utilization of the available heat exchange surface. In case of the arrangement according to the invention, a part of the slantingly disposed condenser block is also below the level of the roof, particularly the part lying forward in the direction of travel, yet the height available for passengers to stand up in the inside space of the vehicle is, however, only slightly decreased and only in the tail area of the vehicle.
In order to keep the longitudinal dimensions of the air-conditioning plant as small as possible, the evaporator part is provided below the condenser part in the direction toward the interior space of the vehicle. In this case, the evaporator blocks are disposed edgewise parallel to one another, in the tail area above the seats, at such a distance in relation to one another that a channel-shaped space is provided between them, which makes it possible that, especially, the height for passengers to stand up in the central aisle area may still be of sufficient dimensions. As a result, an air-conditioning plant that is very compact in its longitudinal dimensions is obtained and a part of it lies below the level of height of the roof, reducing its overall height on the vehicle.
In order to increase the efficiency of the condenser, the condenser fans are disposed in the tail area of the vehicle behind the large-surface condenser block so that an exceedingly favorable flow with little resistance through the condenser part, from its inlet to its outlet, is obtained. Since the air-conditioning plant extends, altogether, to the tail part of the motor vehicle, the carrying off of rainwater from the part of the condenser projecting beyond the level of the roof will cause no problems, since the rainwater can be carried off over the back pane without the use of drain hoses in the body of the vehicle. The extremely favorable flow through the condenser with little resistance may also be accompanied by advantages so that, dependent on the outside temperature and possibly on the speed of travel, sufficient condenser cooling will be ensured even when the condenser fan is turned off.
Whenever, then the air-conditioning plant is capable of operating with a turned off condenser fan, the useful life of the driving motors of the condenser fan will be improved, the need for current taken from the power supply of the vehicle will be reduced and the air-conditioning plant may be operated in an energy efficient manner. Furthermore, the air-conditioning plant, especially the condenser part and the evaporator part of it, has such dimensions that it may be integrated into the structure of the roof in the tail area of the vehicle in a manner that the longitudinal spars of the roof skeleton remain unchanged and only individual spars will possibly have to be changed but then, however, such spars may be made a component of the housing or may constitute the structure for accommodation of the air-conditioning plant. Despite the relatively slight constitutional length and width of the air-conditioning plant, one will obtain a high cooling performance which may be 23 Kw and greater.
Additional advantageous aspects of the invention include the fact that suction spaces of the evaporator part are developed running continuously in a longitudinal direction in parallel to the evaporator part are developed running continuously in a longitudinal direction in parallel to the evaporator blocks, so that suction spaces that are as large as possible with lowered resistance will be available. At the same time, the lateral surface limiting the channel-shaped interval between evaporator blocks may be used, also, in this case in an advantageous manner, which may be covered with a grid, for example, as a closure screen.
In accordance with embodiments of the invention, the condenser fans are disposed side-by-side transversely to the direction vehicle travel with the fan axles disposed horizontally in parallel to the vehicular travel direction. The air flow resistance from the inlet to the outlet of the condenser will be decreased further by such an arrangement since no deflection of exhaust air is provided, the condenser fans conducting the exhaust air of the condenser horizontally to the outside.
The front side of the housing surrounding the condenser fans may terminate approximately in an extension of the tail surface of the vehicle, in which case the rainwater may be conducted away from the condenser over the rear window of the vehicle in such a way that no rainwater can reach the condenser part of the air-conditioning plant.
With an embodiment of the air-conditioning plant according to the invention, wherein the housing surrounding the condenser fans is enlarged transversely to the vehicular travel direction relative to the condenser block, and the condenser fan axles are disposed approximately in the middle of the total height of the condenser and evaporator parts. In this respect, six condenser fans may be disposed so as to achieve an efficient air-conditioning plant without difficulties, the fans being distributed over the width of the tail of the vehicle without the height of the super structure being greater than that of the remaining part of the air-conditioning plant, especially of the condenser.
In accordance with further developments of the invention, the evaporator fans, which are formed preferably by double radial fans, are arranged such that the conditioned air, after passage through the evaporator blocks, may be introduced approximately in a horizontal flow into the air channels of the vehicle, likewise without any noteworthy deflection. In the case of the air-conditioning plant of the invention, the evaporator is arranged approximately in a horizontal plane starting out from the intake area up to the air channels. As a result of that, an even through-flow of the evaporator part with little resistance will be ensured.
Still further, heating batteries may be provided in the evaporator part which have the task of heating up the conditioned air, prior to its introduction into the air channels, whenever said air has been cooled too much during the through the evaporator blocks.
In an alternative embodiment for the reheating of conditioned air, the condenser exhaust air, which is warm, is used. Since, in the case of the air-conditioning plant designed according to the invention, the condenser and the evaporator are disposed directly adjacent to one another, but are largely partitioned relative to each other, one may achieve such a reheating simply by the fact that by means of regulating arrangements, the condenser exhaust air is mixed with the conditioned air prior to entry into the evaporator fan.
In accordance with another feature of the invention, a fresh air part is integrated into the total installation that extends, as a roof-top part, parallel to the condenser block up to the housing part that accommodates the condenser fan. This fresh air part makes it possible to feed in fresh air in a manner that is protected against rainwater and, especially, is free to pressure head across the fresh air channels which extend on both sides of the condenser trough of the condenser. The air channels are open in the front and the rear so that, in the area of the fresh air feed-in, no pressure head occurs. Furthermore, a connection with the intake area exists in front of the evaporator blocks by way of a spacing between the bottom of the condenser trough of the condenser part and the upper part of the condenser blocks. The portion of fresh air in this case is regulatable by means of a system of flaps.
As previously indicated, it is advantageous for the condenser block to be angled. For the angle of inclination of the condenser block with which one may ensure good cooling performances without increasing excessively the air resistance coefficient value C.sub.w for the motor vehicle, an angle of up to 20 degrees from horizontal, preferably 5 to 12 degrees and, especially 3 degrees is used.
In accordance with yet another aspect of the invention, the parts of the air-conditioning plant, condenser, evaporator, and fresh air part are disposed symmetrically to the central longitudinal axis of the roof of the vehicle, so that a pre-assembled construction unit, ready for mounting, may be installed with the use of longitudinal spars of the roof frame, which spars possibly may be integrated without difficulty into the housing construction of the air-conditioning plant as a carrier. The parts of the air-conditioning plant projecting into the interior passenger space are dimensioned such that they fit into the space existing between the longitudinal spars of the frame of the roof and pass through said space.
In the case of a specific embodiment of the air-conditioning plant of the invention, a cooling performance of 23 Kw and greater will be achieved with a short constructional length and a short width through the use of 3 double radial evaporator fans and six condenser fans. The elevation of the construction, altogether, above the contour of the roof, in this case, is approximately 127 mm. the length of the air-conditioning plant may be changed at any time corresponding to the required performances without the height and the width of the installation having to be changed.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.